The present invention is directed to the field of cochlear implants for patients with hearing impairment and/or tinnitus, more particularly to a transcanal, transtympanic cochlear implant system that requires a minimum of surgical intrusion that may be performed at a physician""s office under local anesthesia.
The present invention relates to a transcanal, transtympanic cochlear implant system ideally suited for those profoundly deaf, where conventional amplifying hearing aids are of limited or no value to those suffering the hearing impairment. That is to say, with maximum gain delivered by the most powerful hearing aids, these profoundly deaf individuals cannot hear sound and hence cannot discriminate and understand speech. In addition, there are an estimated 200-300 million people who have various patterns of severe sensorineural hearing loss, which are imperfectly rehabilitated via hearing aids. An example of such is so called xe2x80x9cski-sloped hearing loss,xe2x80x9d where there is near normal hearing in the low to middle frequency range, but the hearing drops out dramatically in the higher frequencies. For these types of hearing loss, amplification is ineffective, because the cochlea cannot perform its transductive function of converting the mechanical energy of sound to the electrical current, which is ultimately perceived as sound by the brain. The inner ear structures responsible for this transductive function are known as hair cells, and the electrical currents, which they produce in response to the mechanical stimulation by sound, are known as cochlear microphonics. When these hair cells are sufficiently damaged in the above mentioned scenarios, no amount of amplification will be effective.
The cochlear implant is, in effect, a bionic ear in that it replaces the lost cochlear microphonic with an electrical current that is the precise analog of sound. Current United States Food and Drug Administration (xe2x80x9cFDAxe2x80x9d) approved cochlear implant systems are so-called multichannel long electrode devices, which are expensive, highly complex devices surgically introduced via a complicated and (for the average otolaryngologist) risky procedure under general anesthesia known as the facial recess mastoidectomy. The estimated cost of these cochlear implant systems, including surgical, anesthesia, hospital, and programming fees is currently quite high. The hardware necessary to program these devices adds further to these high costs, and the time to program the first map for these devices averages from four to twelve hours depending upon the age of the patient, among other factors. This prohibitive price and impractical complexity is simply not accessible to the vast majority of the global deaf population. Furthermore, the average otologist in the developing countries of the world typically does not have the sophistication, expertise and equipment to confidently undertake the facial recess mastoidectomy in order to introduce the internal component of the multichannel systems.
The most tragic irony of all is that the multichannel long electrode devices can destroy residual hearing when they are inserted into the cochlea. This well acknowledged fact makes these devices difficult to justify in very young infants where the precise degree of hearing loss is often in doubt. Furthermore, they cannot be used for ancillary applications for partial hearing loss aforementioned or for the electrical suppression of tinnitus in serviceable hearing ears. In contrast, the transcanal middle ear cochlear implant system of the present invention is a safe, accessible, and cost effective system in which the internal device can be surgically introduced in an office setting under local anesthesia. As will become apparent hereafter, surgical risk to the facial nerve and inner ear are thus greatly diminished. Postoperative healing and recovery times are greatly lessened, and thus time to hook up and program the external device are significantly shortened. Because the internal device resides in the middle ear and does not significantly damage residual hearing, ancillary uses of the system for applications such as ski sloped hearing loss and the electrical suppression of tinnitus become possible and practical.
The theory behind the use of multiple electrodes is based upon the so-called tonotopic theory for the normally functioning cochlea. That is to say, the normally functioning cochlea mechanically sorts sounds according to their frequency, so that the highest tones vibrate the basilar membrane closer to the round window (lower down in the cochlea) and the lower tones vibrate the basilar membrane closer to the apex of the cochlea. Multiple electrodes thus necessitate a longer electrode to be inserted into the cochlea so that multiple electrodes (sometimes referred to as channels) can deliver specific portions of the frequency spectrum to specific sections of the basilar membrane. Thus, the damaged cochlea is postulated to be analogous to a piano; it does not matter so much how hard we press the keys or at what speed. The critical factor is to press the keys at the right spot on the piano in order to get the proper tone or frequency.
Although presently somewhat controversial, there is ample evidence to discredit the validity of the tonotopic theory for the damaged cochlea. Numerous temporal bone studies of deceased cochlear implant patients have repeatedly shown that few if any of them have any stimuable dendrites remaining in the basilar membrane, i.e., to continue the analogy, the piano keys are missing. In fact, it is now commonly accepted that the more central spiral ganglion nerve cells are the site of stimulation. The facts are that the practice was to initially develop long electrode, multiple channel arrays to conform to a theory, which though accurate and valid for the normally functioning cochlea, is invalid for the damaged cochlea. Nevertheless, these systems work and work well, which is a testament to the remarkable plasticity of the neural pathways and brain. Equally remarkable, a short electrode inserted into the cochlea delivering an exact electrical analog of sound can afford the patient the very same pitch discrimination as multiple channel systems. Several drawbacks to multiple channel systems are: (1) multichannel technology is presently very expensive; (2) multichannel systems are very complex which begets system failures over time; (3) energy requirements for the multichannel systems are high and consequently battery life is lower; and, (4) most important of all, multichannel long electrode arrays can, and often do, damage residual hearing.
Notwithstanding, but, rather because of current orthodoxy, multichannel systems are in current favor. Because multichannel systems necessitate long electrode arrays, the surgical introduction of the internal device requires the more complicated facial recess mastoidectomy in order to technically insert this electrode array properly within the cochlea. A multichannel long electrode could not be inserted via a transcanal approach. Furthermore, the electronics package and receiver coil for such a complex sound-processing scheme would not fit within the middle ear space.
Because these multichannel systems damage residual hearing, they have to date not been useful in combination with hearing aids for selective frequency losses, nor have they been used for the electrical suppression of tinnitus in serviceable hearing ears.
Examples of the prior art, as reflected in the following U.S. Patents, describe several of these multichannel type cochlear implant devices. Such prior art patents are summarized and believed to operate as follows:
a) U.S. Pat. No. 6,289,247, to Faltys et al., relates to a universal strategy selector (USS) for use with a multichannel cochlear prosthesis that includes (a) a processor, or equivalent; (b) a selector; and (c) a display. The multichannel cochlear prosthesis is characterized by multiple stimulation channels through which a specific pattern of electrical stimulation, modulated by acoustic signals, and in accordance with a selected speech processing strategy, may be spatiotemporally applied to a patient""s cochlea in order to yield speech intelligibility. The processor of the USS includes appropriate processing means coupled to the multichannel cochlear prosthesis for defining one of a plurality of speech processing strategies for use by the multichannel cochlear prosthesis. In one embodiment, the processing means is realized using a personal computer (PC) programmed with appropriate software. The speech processing strategy that may be selected by the USS may be selected from a multiplicity of speech processing strategies. In one embodiment, the multiplicity of speech processing strategies includes at least one simultaneous speech processing strategy, such as simultaneous analog stimulation (SAS); and at least one non-simultaneous speech processing strategy, such as a continuous interleaved sampler (CIS); and at least one strategy whose temporal characteristics lie somewhere in between simultaneous or non-simultaneous, and whose stimulating waveform(s) may comprise a hybrid combination of analog and/or pulsatile waveforms. In another embodiment, the speech processing strategy that may be selected by the USS is selected from a plurality of speech processing strategies of the same type, e.g., pulsatile strategies. The selector of the USS comprises a switch, pointer, or other selection means, for manually selecting one of the multiplicity or plurality of speech processing strategies as the selected speech processing strategy. The display of the USS, which is controlled by the processing means, provides a graphical or visual representation that characterizes the selected speech processing strategy in terms of representative stimulation waveforms and electrode coupling (e.g., bipolar or monopolar) for each channel.
b) U.S. Pat. No. 5,938,691, to Schulman et al., teaches a cochlea stimulation system which includes a patient wearable system comprising an externally wearable signal processor (WP) and a headpiece in electronic communication with an implanted cochlear stimulator (ICS). The ICS comprises eight output stages each having two electrically isolated capacitor-coupled electrodes, designated xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d circuits for monitoring the voltages on these electrodes, and circuits for both transmitting status information to and receiving control information from the WP. Based upon information received from the WP, a processor within the ICS can control both the frequency and the widths of the output stimulation pulses applied to the electrodes and may select which electrodes to monitor. The ICS receives power and data signals telemetrically through the skin from the WP. To save power, the ICS may be xe2x80x9cpowered downxe2x80x9d by the WP based upon the absence of audio information or xe2x80x9cpowered upxe2x80x9d if audio is present. The WP communicates with the headpiece over a co-axial cable using one frequency for transmitting signals and a second different frequency for receiving signals.
c.) U.S. Pat. No. 5,749,912, to Zhang et al., discloses a low-cost, four-channel cochlear stimulation system utilizing a completely passive, implantable receiver/electrode array that is inductively coupled to an external wearable processor. The receiver/electrode array is formed in a silicone rubber carrier adapted to be implanted in a deaf patient. At one end of the receiver/electrode array, positioned subcutaneously near the surface of skin above the ear, four receiving coils are arranged in an appropriate pattern. Such receiving coils are held within an hermetically-sealed titanium case. At the other end of the receiver/electrode array, which may be preformed in a spiral to match the basal turn of the cochlea, and which is inserted in the cochlea, four ball electrodes are spaced apart along an inner radius of the spiral. Each electrode is electrically connected to a respective receiving coil. Each receiving coil is also electrically connected to a reference electrode typically located near the receiver-coil end of the array. The wearable processor senses audible sounds, converts the sensed sounds to corresponding electrical signals, and splits the electrical signals into four frequency bands or channels. A speech processing strategy applies the processed signals of each channel to each of four external coils, as a series of biphasic current pulses. The four external coils are aligned, using a suitable headpiece, with corresponding coils of the receiver/electrode array, thereby inductively coupling the biphasic current to a respective electrode of the implanted electrode array.
Some additional earlier work in developing hearing improvement to humans may be found in the following U.S. patents:
a.) U.S. Pat. No. 4,696,287, to Hortmann et al., teaches an implanted hearing aid for deaf patients having an intact auditory nerve and includes an implanted receiver unit provided with a receiver coil surrounding the patient""s external auditory canal. An external transmitter unit is electrically connected to a separate transmitter coil embedded in a fitting piece insertable into the external auditory canal in the range of the receiving coil so as to establish an optimum inductive coupling. A microphone is supported on an ear yoke and connected both to the transmitter and the receiver units. The receiver unit is electrically connected to an excitation electrode mounted in the cochlea in the patient""s ear.
b.) U.S. Pat. No. 4,419,995, to Hochmai, et al., relates to a chronic auditory stimulation system that is achieved by establishing an electric field at the base of the cochlea whereby full speech patterns are imparted to a patient. Penetration of the cochlea is not required thereby reducing the risks in installing the implanted electrodes. In one embodiment, thereof, the electrodes are disc shaped with the ground electrode being larger than the active electrode. The active electrode is preferably placed in the round window at the base of the cochlea or on the promontory. The ground electrode is placed 2-10 mm from the active electrode to thereby confine the electric field. The interconnections to the electrodes are tissue compatible covered wires thereby minimizing stimulation of cutaneous nerve fibers.
The foregoing patents relating to various multichannel and single cochlear implantation devices, though teaching systems employing mechanism to help the hearing impaired, teach complex and costly mechanisms that require, above the financial impact, patient convalescence of an inordinate amount of time. It would be desirable to have a transcanal, transtympanic cochlear implant system that involves a minimum of invasive surgery, more specifically, a surgical procedure that may be performed in a doctor""s office. The manner by which the present invention accomplishes the goals hereof will become apparent in the description which follows, particularly when read in conjunction with the accompanying drawings.
The present invention provides a transcanal, transtympanic cochlear implant system for the rehabilitation of deafness and tinnitus that is safe and cost effective, and features a practical and short electrode receiver device, which can be introduced under local anesthesia in a doctor""s office via tympanotomy. It can be used to deliver pure analog electrical currents, such as single channel sound processing strategy, or fractionated electrical currents (multichannel strategy) via a unique, multi-purpose J-shaped short electrode. Such electrical currents have diverse applications in the rehabilitations of various degrees of sensorineural hearing loss and its manifestations, i.e., tinnitus, because its short electrode does not damage residual hearing.
The system of the present invention comprises two major components, specifically an external sound processor and a surgically implanted middle ear component. The first component, for removable positioning within the auditory canal, comprises a sound processor containing at least one microphone for receiving sounds, means for demodulating the sound to an electrical digitized signal, means for converting the digitized signal to an electromagnetic signal, and a portable electrical power source, such as a battery. The second component for implantation within the middle ear space, comprises an insulated receiver coil for receiving electromagnetic signal, where the receiver coil is disposed between a pair of bones within the inner ear, and a wire mesh electrode located within receiving coil which functions as a ground electrode. In another embodiment the second component includes an application specific integrated circuit, and a J-shaped electrode extending therefrom.
Accordingly, a feature of the present invention is the provision of a transcanal, transtympanic cochlear implant system that may be implanted within a patient""s inner ear with a minimum of invasive surgery, a procedure that can be performed in a doctor""s office under local anesthesia.
Another a feature of the present invention is a cochlear implant system that includes a uniquely constructed, insulated receiver coil for receiving an electromagnetic signal for transmission to the cochlea and the perilymph fluids contained therein.
A further feature of the present invention is the provision of a molded insert for positioning within the auditory canal of the human ear, where the insert includes a microphone for receiving sound to be demodulated to an electrical digitized signal, which in turn is converted to an electromagnetic signal, thence transmitted to the cochlea.
These and other features of the present invention will become more apparent in the specification and accompanying drawings which follow.